1. Field of the Invention
The invention generally relates to recording and/or reproducing apparatus for use with a flexible storage medium, such as a pliable magnetic disk, and, more particularly, to a double-sided recording device having magnetic heads disposed on opposite sides of the disk.
2. Description Relative to the Prior Art
Double-sided recording on a floppy disk has been used to increase capacity and facilitate data transfer operations. Contact is generally maintained on both sides of the disk at the same time and in the same general location. A typical double-sided contact system is disclosed by U.S. Pat. No. 4,151,573, which shows a fixed head on one side of a disk and a cantilevered, gimbal-mounted, movable head on the other side. In operation, the disk is confined againt the fixed head, despite perturbations in movment of te disk, by the pressure of the movable head.
Typically, the disk is contained within a protective plastic jacket. A shutter on the jacket is moved aside to reveal a windowed opening through which the heads can contact the disk. For double-sided recoding, inasmuch as the window is quite small, the heads are ordinarily in direct opposition or slightly offset in a radial direction to avoid flux interaction. This arrangement is desirable in any case because the disk, according to the prior art, is urged against one head by the force of the other--as further illustrated by U.S. Pat. No. 4,320,426, in which the disk is conformed to a wavy contour where it is captured between two radially offset heads.
If the radial offset is increased, other means must be provided to effectively capture the disk. For example, in the double-sided head structure described in U.S. Pat. No.4,074,331, each head employs a pressure pad positioned on the opposite side of the disk to urge the disk into recording contact with the head. As there are two heads and two pressure pads, when one head is selected to be operative, the other pressure pad is pivoted away from the disk and the other head loses effective contact with the disk.
A series of patent disclosures (beginning with U.S. Pat. No. 4,578,727--which discloses a single-sided contact recording device) describe a head stabilizing structure which achieves a stable, constant interface between a moving disk and a magnetic head without the necessity of backing the disk with a pressure member. Such a stable interface is established by surrounding the transducing surface of the magnetic head with a small, flat air bearing surface on one side of a stabilizer block. In companion U.S. Pat. No. 4,620,250, the air bearing surface is disposed at an angle with respect to the disk so that a leading edge of the air bearing surface penetrates slightly into the nominal plane of the rotating disk. This is believed to assist in the formation of strong coupling forces along the air bearing surface.
In Ser. No. 176,964, filed Apr. 4, 1988, this teaching is applied to a pair of oppositely-disposed stabilizer blocks that support opposed magnetic heads for simultaneously interfacing with opposite sides of a rotating magnetic disk. The flat, circumferential air bearing surface on each block generates coupling forces that deform the disk out of its nominal plane on opposite sides thereof and into intimate contact with the transducing gaps on the respective heads. The stabilizer devices are positioned in relation to separate radii depending from the center of the drive spindle so that a circumferential offset is established that permits substantially separate, but simultaneous, interaction of the air bearing surfaces with the disk.
The air bearing surface has been further refined both as to shape and composition in U.S. patent application Ser. Nos. 19,468 and 136,793 (filed respectively on Feb. 26, 1987 and Dec. 22, 1987, and both assigned to the assignee of the present invention). The stabilizer is accordingly improved by establishing an abrupt transition in the leading edge of the air bearing surface that penetrates the nominal plane of the moving disk. The transition appears to act as a fulcrum, generating a force that turns a section of the moving disk about the transition and flattens the disk down upon the head. This force contributes to the coupling forces seen in the prior devices. The stabilizer is further improved if made from a ceramic material, such as barium titanate. A stabilizer of such material is operative for long periods with relatively low frictional drag between the disk and the air bearing surface, a condition that lowers current draw upon the disk drive motor.
Double-sided recording using the above-described stabilizer blocks requires an offset between the air bearing surfaces so that a stable interface is maintained between each head and the disk. Unlike other forms of conventional double-sided recording, the opposed air bearing surfaces are intolerant of close interaction and must be displaced relative to each other if both are in simultaneous contact with the disk. This tends to take up quite a bit of space and can be a problem if the windowed opening in the jacket is too small to accommodate both stabilizer blocks.